Does Fish Oil Thin the Blood?

Fish oil can have varying effects on blood clotting.

Omega-3 fats such as fish oil may help lower inflammation and triglycerides, keep your brain healthy and lower your heart disease risk, reports the University of Maryland Medical Center. They may also have a blood-thinning effect, however, so only use fish oil supplements after discussing their safety with your doctor.

Potential Effects

Consuming more than 3 grams per day of fish oil may make your blood less likely to clot and make you more likely to suffer from increased bleeding, notes MedlinePlus. Fish oil supplementation, however, doesn't seem to prolong bleeding time enough to cause the potential hemorrhages and bruising sometimes associated with blood-thinning medications, at least not in healthy people, notes an article published in "The Journal of Nutrition" in March 2003.

Probable Mechanisms

Study results are conflicting on how fish oil affects blood clotting. Vitamin K is essential for blood clotting, so blood-thinning medications are often designed to limit vitamin K's blood-clotting ability. While the 2003 "Journal of Nutrition" article notes that fish oil appears to decrease the activity of the blood-clotting factors that depend on vitamin K, another study published in "Arteriosclerosis, Thrombosis, and Vascular Biology" in 2004 found that fish oil only affected clotting factors not dependent on vitamin K. These factors include a protein called fibrinogen and a substance called factor V. Thus, vitamin K consumption might not reverse the effect of fish oil on blood clotting, as it does with blood-thinning medications.

People Affected

The blood-thinning potential of fish oil benefits people who have an increased risk for heart disease because reducing the risk for blood clots helps limit clogging of the arteries, making heart attacks less likely. Not all people experience the same effects when taking supplemental fish oil, however. For example, people with higher triglyceride levels may experience greater effects on both triglyceride levels and blood thinning from taking fish oil than those with lower triglyceride levels, according to a study published in "The Journal of Nutrition" in January 2007.

Other Considerations

If you take blood thinners, fish oil may interact with them and cause your blood to become thinner than it should. It can also interact with other medications, including blood pressure drugs, birth control pills and orlistat. People suffering from bipolar disorder, diabetes, high blood pressure, liver disease or certain other medical conditions may need to avoid taking fish oil, as it could cause adverse effects or worsen their condition.